Update data_analytics_dag.py again (#8017)
Update data_analytics_dag.py again (#8017)

Need to use write_append to concatenate all of the tables, my bad. It's okay to have it keep adding the data for the sake of our demo.

GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples